Stare Decisis

Stare decisis is a legal principle by which judges are obliged to respect the precedents established by prior decisions.The principle of stare decisis can be divided into two components.The first is the rule that a decision made by a superior court is binding precedent which an inferior court cannot change. The second is the principle that a court should not overturn its own precedents unless there is a strong reason to do so and should be guided by principles from lateral and inferior courts.When judges try cases they must check to see if similar cases have been tried by a court previously. If there was a precedent set by an equal or superior court, then a judge should obey that precedent. If there is a precedent set by an inferior court, a judge does not have to follow it, but may consider it.

source: http://en.wikipedia.org/wiki/Stare_decisis